Montauk template, purchase page image format from square to native

When customers click on an image in the products gallery, they are taken to a purchase page where they can choose one of two print sizes. The problem is that the preview on that page is a cropped square, and my photographs are either horizontal or vertical. This square preview gives a false impression of what the customer is purchasing and, since migrating to SS, has greatly diminished my print sales.

Can I add code to change the image from filling to preview block to just fitting the image file within the block?

I don't want to change hosts again, but I might have to.